Circulatory and metabolic responses to carbon monoxide hypoxia during beta-adrenergic blockade

The role(s) of beta-adrenoceptors in whole body and hindlimb skeletal muscle cardiovascular and metabolic responses during carbon monoxide hypoxia (COH) was studied in anesthetized dogs. One group of animals was beta-blocked with propranolol (beta 1- and beta 2-blockade), a second was given ICI 118,551 (beta 2-blockade), and a third served as a time control. Immediately after a control-sampling period, COH was induced (about a 63% decrease in arterial O2 content), and additional measurements were then obtained at 30 and 60 min of hypoxia. Cardiac output values were not different between the three series at control; an increase (P less than 0.05) occurred in all groups during COH. This rise was greatest in the COH group; the values for the propranolol- and ICI 118,551-blocked groups were not different from each other during COH. Hindlimb blood flow rose (P less than 0.05) during COH only in the control group. Both whole body (30 min) and hindlimb (30 and 60 min) resistance values were greater during hypoxia in the beta-blocked groups (P less than 0.05) than in the control series. Furthermore, whole body oxygen uptake decreased (P less than 0.05) in both beta-blocked groups during COH. We conclude that approximately 35% of the rise in cardiac output occurring during COH depended on peripheral vasodilation mediated through beta 2-adrenoceptors.